Cigarette smoking is the leading preventable cause of death in the US. Although 7 out of 10 smokers want to quit, less than 5% of quit attempts remain successful one year later. Smartphone apps are a promising method to deliver behavioral interventions due to their immediate accessibility, reduced barriers to treatment, and high penetration of the target population. The goal of this SBIR is to reduce the health impact of smoking by establishing Click Therapeutics, Inc.?s smartphone app for smoking cessation, Clickotine (CKT), as a digital therapeutic solution to help smokers quit with lower cost, reduced need for healthcare access, and fewer adverse effects than current best alternatives. CKT follows US Clinical Practice Guidelines (USCPG) for smoking cessation and uses interventions supported by research: personalized messaging, controlled breathing, social engagement, treatment adherence, financial incentives, and digital diversions. Short-term quit rates observed in a pilot clinical trial of CKT compare favorably to published results of other smartphone apps for smoking cessation. However, to date no such studies have provided biochemically verified evidence for long-term quit rates, which forms the gold standard for measuring other therapies for smoking. This project will address this gap in knowledge through blinded randomized controlled trials comparing CKT to another widely used USCPG smartphone app, the National Cancer Institute?s QuitGuide. This pivotal research will feature longer-term follow-up and biochemical verification with feasibility established in Phase I. The results of this study will provide the rigorous clinical evidence for the efficacy and safety of CKT necessary for its successful commercialization in the digital therapeutics market. Wide availability of an engaging, low-cost mobile intervention to help smokers quit with reduced healthcare usage will have substantial population-level impact on public health in the United States.